Biomedical Engineering Reference
In-Depth Information
Fig. 30.2
Architecture of a short pulse DWA for proton therapy. The beam tube with diameter b
is a high gradient insulator. The vertical lines indicate the conductors of the transmission lines that
supply pulsed voltages across the HGI. The arrows denote the tangential electric field along the
insulator surface that provides the acceleration of the particle bunch
effects enhancing the field by a factor of about 10 to 300 MV/m, which is in excess
of the bulk breakdown strength of the material. The group is currently working on
developing an enhancement free, integrated switch package [
16
].
A test system named F.A.S.T. for First Article System Test [
16
] comprising
a small number (7) of Blumleins, photoconductive switches, and a high gradient
insulator tube has been constructed and serves as testbed for the fully integrated
system. The number of Blumleins, and thereby the maximum acceleration achiev-
able, has been kept small to allow easy disassembly and repair in case of failure on
some components. In order to accelerate protons through F.A.S.T. an initial velocity
sufficient to cross the HGI gap during the 3 ns pulse duration, requiring at least
200 keV at the entrance of F.A.S.T. is required. This was achieved using 5 20 ns
induction cells.
The technology, showing a clear promise towards a lightweight, compact
(2 meters or less) source of 200 MeV protons, could potentially revolutionize
proton beam cancer therapy, making it available to small hospitals and private
clinics, as the foreseen size of the overall system would allow to retrofit existing
IMRT installations to provide intensity modulated proton therapy (IMPT) instead.
But before patients could benefit from protons accelerated by a Dielectric Wall
Accelerator many steps beyond achieving the required energy will be necessary.
Exact dosimetric information for the beam from the DWA will need to be
established. Beam delivery concepts and treatment planning studies need to be
performed and verified by in-vitro and in-vivo experiments. As with all projects
relying on new technology, it is not possible to predict when it will become available
commercially, but strong commercial interest is exemplified by Tomotherapy, Inc.
joining the effort and providing partial funding of the continuing development. An
artist's conception of such a future installation is shown in Fig.
30.3
.
30.3.2
Laser Plasma Accelerators
If a high-intensity laser [
22
] or a particle beam [
23
] passes through a plasma, a
fast, large amplitude plasma wave, also known as a wakefield, is generated. Field
